Bernd Heinrich - Summer World: A Season of Bounty (P.S.)

Introduction

M ARCH OFTEN BRINGS HEAVY SNOWFALLS HERE in Maine and Vermont. Its cold outside and I spend much of my time behind windowpanes in a bubble of tropical environment created by our wood-burning stove. Im waiting for summer. Here in the north temperate zone, summer usually lasts for roughly half the year, from May through October. Its the time most of us (who are not recreational skiers) live or at least wait for.

Day after day I gaze at the white expanse of the beaver bog by our house to wait and hope for the red-winged blackbirds to return. Instead, in my minds eye during March I see a family of beavers entombed in their lodge, which sticks up like a big lump above the thick snow-covered ice on the pond. The beavers bubble for sustainable life is now a mere platform of sticks inches above the ice-cold water. Its barely large enough to move around in, and they live there in continuous darkness. Occasionally one or another of the beaver family holds its breath for several minutes as it dives into the hole next to its platform that is kept ice-free, to bring back a twig and chew off the bark. I identify with these beavers, because like theirs, much of my living is, for months, repressed and in my own bubble. Summer releases it.

The world right now seems dead, but some birds are already stirring. Hairy and downy woodpeckers have started to drum; black-capped chickadees sound off their dee-dahs at dawn; and the first robins have returned, and they hop where snow has melted along roadsides. Dawn is a bit earlier each day, and I awake with yearning and anticipation.

In my nostalgia for summers past and anticipation of summers to come, I think of swimming, basking in the sun while wiggling into warm sand at the beach, and reveling in the sights, sounds, and smells of flowers, bees, and birds. I think of the dances on balmy nights as we swung and do-si-doed our partners and sweated to fiddle music at the town hall; and of bass fishing on Bog Stream, where we canoed past floating lily pads and big white water lily blossoms. I think of the school year coming to a close.

For me, summer used to begin on the first day of school vacation, the season of long days. A more universal and just as specific beginning of summer (in the northern hemisphere) is probably around 20 March, the vernal (spring) equinox (equal night), when the night and the day are the same length. The height of northern summer is near 21 June, the summer solstice (corresponding to the winter solstice in the southern hemisphere), when in the north the days are the longest and we receive the most sunshine in the year. However, this is designated as the beginning of summer, not the height, because the maximum warmth is yet to come; it takes about a month and a half before the northern lands and oceans, still cold from the winter, have reheated. Then, after the summer solstice, the days shorten until about ninety-four days later, on 22 September, when they are again equal. On 21 December, the winter solstice, the days are shortest. Again, owing to the temperature lag from the just-cooled earth and ocean, this date is called the beginning of winter, not its peak.

Almost all of life on the surface of the earth is fueled by the enormous amounts of energy intercepted from the sun, through a chemical reaction involving one main molecule, chlorophyll, and its reaction with water and carbon dioxide to produce sugar, the main fuel that powers life. The process that produces it is photosynthesis, meaning, literally, making from photons. The amount of this energy that continually streams onto Earth, and is proximally fixed into sugar, is relatively constant throughout the year, but the portion that is captured in any one place on Earth at any one time depends largely on the daily duration of illumination, and the angle at which the rays hit the Earths surface.

Both the duration and the incidence of illumination at any one place depend on the Earths tilt, or inclination, toward the sun, and the seasons are a consequence of this tilt. At all points of the Earths approximately 365-day (actually 365.2422-day) orbit around the sun, which we define as a year, the Earths axis of rotation (an imaginary line connecting the north and south poles) is 23.5 degrees with respect to the plane of its orbit around the sun. This angle does not affect the total energy that the entire Earth receives over the year; rather, it shifts the distribution of energy between the northern and southern hemispheres. When one hemisphere gets a lot of energy, the other gets little, and thus when it is summer in one it is winter in the other. At the equator the energy input is equal year-round, the sun is directly overhead at noon, and days and nights are always equal.

When the Earth is at the point in its orbit where the north pole is inclined at its maximum, 23.5 degrees, toward the sun, that is defined as the summer solstice in the north. At this time the far north is in continuous light and the far south is in continuous darkness. As the Earth continues its journey around the sun (while still maintaining its own same axis of rotation) the tilt that was toward the sun decreases gradually until solar radiation falls equally slanted onto both poles. At this point, the autumnal equinox, day and night are of equal length everywhere.

The solstices, the asteorological relationships during the Earths annual journey around the sun, proximally cause the seasons and the overall weather patterns to which life adjusts. However, ultimately the seasons are due to an ancient catastrophe. Astronomers believe that about 4 billion years ago a body the size and mass of Mars slammed into the Earth at 18,000 miles per hour, possibly tipping the Earths axis of rotation. Additionally, the matter that was ejected by this colossal collision produced the moon. Life arose near that time, about half a billion (500 million) years later, and it has adjusted to summer versus winter ever since. Different species each have their own schedules of preparation for summer, although for most summer is the season of reproduction, feeding, growing, and trying to avoid being eaten. Its the season of courting, mating, and birthing; of living and dying.